In particular, in a disc brake, the brake caliper is arranged astride of the outer peripheral edge of a brake disc. The brake caliper usually comprises a body having two elongated elements that are arranged so as to face opposite braking surfaces of a disc. Friction pads are foreseen arranged between each elongated element of the caliper and the braking surfaces of the brake disc. At least one of the elongated elements of the body of the caliper has cylinders suitable for receiving hydraulic pistons capable of exerting a thrusting action on the pads abutting them against the braking surfaces of the disc to exert a braking action on the vehicle.
The brake calipers are usually fixedly connected to a support structure that stays still on the vehicle, like for example a stub axle of a suspension of a vehicle.
In a typical arrangement, one of the two elongated elements has two or more mounting portions of the body of the caliper to the support structure, for example foreseeing slots or eyelets, for example arranged axially, or through-holes, for example arranged radially, suitable for receiving screws for attaching the caliper that, with their ends, are received in threaded holes foreseen on the support of the caliper.
In a typical caliper body construction, the elongated elements arranged facing the braking surfaces of the disc are connected together by bridge elements arranged astride of the disc.
A caliper body of this type is described in EP-A-2022999. In FIG. 1 of EP-A-2022999 a caliper body of the type with a fixed caliper is shown. This caliper body is of the monoblock type comprising two elongated elements the ends of which are connected together by bridges. Stiffening shafts extend between the elongated elements and between the two bridges forming a cross-type structure.
The caliper comprises different components mounted on the body such as pistons, gaskets, draining devices and brake fluid supply ducts.
Typically, the body of the caliper is made from metal like for example aluminium, or aluminium alloy or cast iron. The body of the caliper can be obtained by fusion, but also by mechanical chip-removal, as well as by forging.
The body of the caliper can be produced both in a single piece or monoblock, but also in two half-calipers typically connected together along a plane that usually coincides with the middle plane of the disc on which the caliper is arranged astride.
In the case in which the driver of the vehicle wants to brake or slow down the travel of the vehicle, he applies a force on the brake pedal, in the case of an automobile. Such a force on the brake pedal, through a brake pump exerts a pressure on the brake fluid that through a duct applies to the brake fluid present in the hydraulic circuit arranged inside the body of the caliper until it reaches the cylinders where the pressure is exerted on the surface of the bottom of the pistons forcing them to clamp against the pads, which in turn abut against the braking surfaces of the disc.
The pressure action of the brake fluid is also exerted on the bottom wall of the cylinder determining a reaction in the body of the caliper that deforms it away from the surfaces of the disc. This deformation of the body of the caliper leads to an increase in the stroke of the pistons and thus to an increase in the stroke of the brake pedal. The body of the caliper also deforms as a function of the torque exerted by the action of the piston that, abutting the pads against the braking surfaces of the disc, applies a deformation moment in directions that form torque arms with respect to the attachment points of the caliper body to its support. These torques deform the caliper body also in a tangential and radial direction with respect to the disc, as well as in an axial direction.
The caliper body must therefore have a sufficient structural rigidity, so as to ensure that this deformation of the body of the caliper caused by the braking action is kept within tolerable values, which, as well as avoiding damage to the braking system, do not create the feeling of a poor braking system for the driver, determining an extra stroke of the lever or pedal of the braking system creating the feeling of a “spongy” system. This requirement pushes towards having extremely rigid structures for the bodies of the calipers and therefore towards increasing their bulk and weight.
On the other hand, the body of the caliper, since it is fixedly connected to the suspension of the vehicle and is arranged astride of the disc, is one of the unsuspended masses that it is wished to reduce as much as possible in order to increase the performance of the vehicle.
Of course, these considerations are taken to the extreme when the vehicle is of the type for racing and the user wishes to have a braking system that is extremely responsive to his commands and at the same time extremely light so as not to penalise the performance of the racing vehicle.
There is therefore a great need for a caliper body for a disc brake that has improved structural characteristics for the same weight of the body of the caliper, or else with the same structural characteristics having a lower weight with respect to the solutions of the prior art. There are known solutions for caliper bodies that are specially studied to increase the characteristics of structural rigidity. For example the aforementioned patent application EP-A-2022999, patent application EP-A-153497, American patent U.S. Pat. No. 6,708,802, European patent application EP-A-1911989, international patent application PCT/EP2005/050615, Japanese patent application JP-A-09257063 and American patent U.S. Pat. No. 3,183,999 all present solutions for bodies for brake calipers equipped with reinforcement elements, for example arranged around the caliper bodies. In some of these known solutions the caliper body is of the symmetrical type according to planes passing through the axis of the disc or through the middle of the disc. In other solutions the caliper body has big and distributed windows that form elongated reinforcement elements arranged longitudinally to the body of the caliper. Although satisfactory from many points of view these known solutions nevertheless do not allow structures to be obtained that maximise the structural rigidity of the body of the caliper, reducing weights and at the same time capable of keeping the bulk as low as possible so as to facilitate the mounting of the body of the caliper even inside rims and wheels on which brake discs having a large diameter are mounted.